Additive effects of sensory contact as a social integration method for captive chimpanzees

Introductions of unfamiliar captive chimpanzees can be a difficult process due to aggression that can result in severe injury or death. Consequently, recommended procedures for chimpanzee introductions have been developed to reduce aggression and facilitate social integration. These procedures gradually increase the amount of sensory contact between the groups prior to direct physical contact. The purpose of this research was to assess these procedures for the introduction of two three year old male chimpanzees to members of a mixed-age maternal group. The procedures involved an additive series of sensory contacts (ie., visual and two limited tactile treatments) that culminated with direct physical contact. Several behaviors were monitored to assess each treatment condition.

A six year old and an eight year old female were selected as appropriate candidates for successive introductions with the infants based on data from the visual contact condition and case history information. For each introduction, the two limited tactile contact conditions produced similar results. Within each condition, prosocial behaviors increased and negative or stress-related behaviors decreased. Differences between the first and second introduction emerged during the direct physical contact condition. For the first introduction, increasing rates of prosocial behaviors and low rates of stress-related behaviors continued from previous conditions. However in the second introduction, behaviors that occurred reliably in the limited tactile conditions reversed or ceased to occur. Aggression and fear-related behaviors predominated the interactions, but were neither severe nor life-threatening. The greatest influence on this appeared to be the behavior of one infant male. His removal from the procedure resulted in rapid increases in prosocial behaviors and decreases in aggression and fear for the remaining individuals.

The data suggest that systematically increasing form of sensory contact does allow introduction candidates to gradually become more familiar, to develop prosocial behavior, and may lessen the severity of aggression during direct physical contact. Continuous monitoring of behaviors was crucial for choosing introduction candidates and deciding when to change conditions. Future replications of this type of research at different zoos are critical to learn more about the mechanisms involved in introductions and how different procedures affect them.